1. Field of the Invention
Embodiments of the present invention generally relate to introducing a gas into a micro cavity to enhance the lifetime of a micro-electromechanical system (MEMS) devices.
2. Description of the Related Art
A digital variable capacitor (DVC) utilizing MEMS technology operates by having a switching element of the MEMS device move between a state of high capacitance and a state of low capacitance. In a state of high capacitance, the switching element is in a position adjacent an RF electrode. In a state of low capacitance, the switching element is in a position adjacent to another electrode spaced from the RF electrode, or more specifically, away from an insulating layer that is disposed on the RF electrode. The switching element may also be moved to ground whereby the switching element is adjacent neither the RF electrode nor the other electrode.
During the lifetime of the MEMS device, the switching element cycles between the various states (i.e., high capacitance, low capacitance and ground). For a cycle, the switching element moves from the ground state to either the high or low capacitance state. After the cycle is completed, and before the next cycle, the switching element returns to the ground state. Then, a new cycle begins whereby the switching element moves to either a high or low capacitance state, or remains in the ground state. This corresponds to a physics movement of a plate which either touches the insulating layer overlying the RF electrode or touches the roof of the cavity in which it is housed.
There are only a finite number of times that the switching element can move before the MEMS device fails. With each movement of the switching element, the MEMS device accumulates a finite amount of damage which, given enough total cycles, results in failure. The magnitude of the finite damage to the MEMS device or the roof of the cavity or the insulating layer overlying the RF electrode is proportional to the impact speed of the fast moving switching element as the switching element is brought into contact therewith. In the above example the contact can cause material to be ejected from the exposed surfaces which then enter between the plates of the capacitor, reducing the closest distance that the ground MEMS plate can make to the insulating layer over the RF electrode. Thus, the maximum possible capacitance is reduced.
Therefore, there is a need in the art for increasing the lifetime of MEMS devices in DVCs by reducing the impact velocity of the switching element in a MEMS device as the switching element makes contact with various surfaces within the device cavity.